UIJKL
The UIJKL file stores the effectively screened Coulomb integrals at the unit-cell origin (R = 0):
- [math]\displaystyle{ U_{ijkl}^{\sigma\sigma'} = \int {\rm d}{\bf r}\int {\rm d}{\bf r}' w_{i}^{*\sigma}({\bf r}) w_{j}^{\sigma}({\bf r}) U({\bf r},{\bf r}',\omega) w_{k}^{*\sigma'}({\bf r}') w_{l}^{\sigma'}({\bf r}') }[/math]
evaluated at zero frequency ([math]\displaystyle{ \omega=0 }[/math]). The columns I, J, K, L are the Wannier function indices; RE and IM are the real and imaginary parts. The format is as follows:
# U_ijkl = [ij,R|kl,0]
# I J K L RE(V_IJKL) IM(V_IJKL)
1 1 1 1 4.3457689208 0.0000000000
2 1 1 1 0.0000021313 0.0000001349
...